Tool checking device for use with numerically controlled machines

Abstract

A sensing assembly is provided which, by utilizing the CNC machine's M-codes, is adapted to be retrofitted to existing numerical control machines for detecting the excessive wear, chipping, breaking or mislocation of the cutting tool and shutting down the CNC machining operation in response.

I claim: 
     
       1. For use with a numerically controlled machine of the type which is programmable to carry out a succession of machining operations on a workpiece, and including means for supporting a workpiece,   tool holder means for releasably securing a worktool and for moving the axially distal portion of said tool against the workpiece to remove material therefrom;   programmable control means responsive to a sequence of programmed instructions for successively positioning the tool holder means with respect to the workpiece and controllably moving the tool against the workpiece during each of a succession of machining operations,   first and second sets of operator-accessible terminal means positioned on the numerically controlled machine for connection to external equipment, and   instruction-responsive means responsive to programmed instructions for producing an operator-accessible signal at the first set of operator-accessible terminal means, and for interrupting the programmed sequence until receipt of an enabling signal,   the second set of operator-accessible terminal means coupling the enabling signal to the instruction-responsive means to initiate the next instruction in said succession;   a retrofit sensor assembly for detecting unacceptable tool length and comprising:   first switch means coupled to the first set of terminal means to selectively apply the enabling signal to the second set of terminal means,   the first switch means being mounted with respect to the numerical control machine to selectively apply said enabling signal to said second set of terminal means only if the axial length of the tool is greater than a minimally acceptable length.   
     
     
       2. The sensor of claim 1 wherein the sensor includes an axially movable plunger positioned for contact by the axially distal end of the tool after a machining operation,   an axially movable plunger positioned for contact by the axially distal end of the tool after a machining operation,   the first switch means is responsive to a predetermined amount of the vertical movement of the plunger to couple the enabling signal to the second set of terminal means, and   the control means is programmed to move the tool holder means after a machining operation to a predetermined position spaced from the plunger means by a minimally acceptable tool length.   
     
     
       3. The sensor assembly of claim 2 including second switch means responsive to the plunger movement for preventing the electrical coupling of the power supply means and the signal-responsive means unless the detected axial length of the tool is less than a predetermined maximum. 
     
     
       4. The sensor assembly of claim 3 wherein the second switch means is coupled in electrical series with the first switch means. 
     
     
       5. The sensor assembly of claim 3, including spring means for biasing said plunger towards an initial position in opposition to the tool-induced movement, the first and second switch means having respective physically movable actuator elements, the plunger including first and second contact surfaces for moving said actuator elements upon respectively sufficient displacement of the plunger by the tool. 
     
     
       6. The sensor assembly of claim 1 including second switch means for preventing the electrical coupling of the power supply means and the signal-responsive means unless the detected axial length of the tool is less than a predetermined maximum. 
     
     
       7. The sensor assembly of claim 6, wherein the second switch means is coupled in electrical series with the first switch means.